B6.Cg-Mtm1^tm1Itl/J

Stock number: 018153
Research areas: Neurobiology Research

Description

These Mtm1 p.R69C mice may aid in the development of therapies for X-linked myotubular myopathy (MTM).

Detailed description

These Mtm1 p.R69C mice contain the p.R69C mutation in exon 4 of the endogenous X-linked myotubular myopathy gene 1 locus (Mtm1). They also harbor a neo cassette, flanked by loxP sites and frt sites, downstream of the targeted mutation. This mutation induces exon skipping of exon 4 and introduces a premature stop codon in exon 5, analogous to a Mtm1 mutation found in humans with X-linked myotubular myopathy (MTM). MTM is a neurodevelopmental disorder which characterized by weakness, hypotonia, external opthalmoplegia, and compromised respiratory function. Hemizygous males are viable but have median survival of 66 weeks due to cardiorespiratory defects. Males are not fertile. These mice exhibit decreased skeletal muscle mass by 2 months of age. They also display defects such as shuffling, widely spaced feet, and chirping. The donating investigator reports no disease phenotype detected in females.
Although hemizygous males may not be used for live breeding, The Jackson Laboratory reports successfully freezing sperm from hemizygous males, and that thawed aliquots of the frozen sperm are viable and fertile for in vitro fertilization.

Development

A targeting construct was designed to insert a loxP/frt-flanked neomycin (neo) resistance cassette downstream of exon 4 of the X-linked myotubular myopathy gene 1 (Mtm1) gene. A c.205C-T point mutation was introduced in exon 4, corresponding to human amino acid 205, resulting in the missense mutation, p.R69C, commonly found in humans with X-linked myotubular myopathy (MTM). This targeting construct was electroporated into C57BL/6 x 129/SvEv-derived embryonic stem (ES) cells and correctly targeted ES cells were injected into C57BL/6J blastocysts. The resulting chimeric mice were bred to C57BL/6J mice. The donating investigator reports mice were backcrossed to C57BL/6J mice for at least ten generations (see SNP results below) prior to sending males to The Jackson Laboratory Repository in 2012. Upon arrival, males were used to cryopreserve sperm. To establish the living mouse colony, an aliquot of the frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664).

A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the first generation rederived living colony at The Jackson Laboratory Repository. While the 26 markers throughout the somatic genome suggested a C57BL/6 genetic background, all 5 markers that determine C57BL/6J from C57BL/6N were found to be segregating. These data suggest the mice sent to The Jackson Laboratory Repository were on a C57BL/6N genetic background.

Allele

Symbol: Mtm1^tm1Itl
Name: targeted mutation 1, inGenious Targeting Laboratory
MGI accession ID: MGI:5307232
Generation method: Targeted
Attributes: Humanized sequence
Marker symbol: Mtm1
Marker name: X-linked myotubular myopathy gene 1
Chromosome: X
Strain of origin: (C57BL/6NTac x 129S6/SvEvTac)F1
Molecular note: Exon 4 was replaced with a modified version in which coding nucleotide 205 was changed from C to T (c.205C>T). This results in the amino acid substitution of arginine with cysteine at position 69 (p.R69C) in the encoded protein. In vivo, however, the mutation results in aberrant splicing, with the majority of transcripts skipping exon 4 (which results in a frameshift and premature termination of translation). The mutation corresponds to one observed in some human X-linked myotubular myopathy (MTM) patients. A loxP site flanked neomycin resistance gene cassette was inserted into intron 4.